The invention relates to an apparatus and a process for removing contaminants from a gaseous stream and more particularly to a scrubber apparatus and process for removing organic dust and mist from a closed loop gaseous stream.
Granulation processes described in U.S. Pat. Nos. 3,877,415; 3,991,225; 4,213,924; 4.424,176; 4,506,453 and 4,507,335 such as for the production of urea and sulphur products use a rotary drum granulator.
In a rotary drum granulation process as described in the above patents, a molten product is sprayed onto a falling curtain of small seed particles and undersize granules to increase the particle size by successive coating of molten material. During the process a tremendous amount of dust particulate and mist can be generated inside the drum. The dust and mist generated in the drum must be separated from any gaseous stream passed therethrough. Equipment external to the granulation drum, such as cyclone separators and bag houses, are commonly used for this purpose. However, these types of equipment for removing dust from the gas stream have not been adequate. It is important to remove the dust and contaminants from the gas stream to minimize the plugging of pipes and downstream equipment outside the drum. In addition, in an enclosed system or closed loop system, it is important to control the dust particles to avoid polluting the atmosphere with the dust or contaminants.
Current granulation cooling gas loop systems utilize a once through air as the coolant. This practice is not universally acceptable for all solid chemicals which might be granulated because environmental constraints or product exposure to the oxygen in air might be unacceptable. For example, because of the above restrictions, a recycle nitrogen as the coolant is used when applied to a bisphenol process.
It is known to use a nitrogen stream as a gas coolant to solidify, by freezing, for example, a molten liquid bisphenol fed to a granulator of a granulation process as described in copending U.S. patent application Ser. No. 005,504, entitled "Production of Granular Bisphenols," filed Jan. 20, 1987 by K. McDonald et al. Shutdowns of a granulation system frequently occur because of a build-up of dust and solids present in the gaseous stream on the surfaces of equipment.
It is, therefore, desired to provide a scrubber apparatus and process to remove dust and solids present in a gaseous stream of a granulation process which will advantageously allow a longer term of operation of a closed-loop nitrogen system without a build-up of dusts and tacky solids which eventually close off duct works of the system.
It is desired to provide an apparatus and process for reducing the amount of dust particles in a gas stream which exits from a rotary granulation drum.
It is further desired to provide a scrubber apparatus and process in which substantially all dusts, mists and solids present in a gaseous stream are dissolved in a scrubber liquid with sufficient levels of caustic present in the scrubber.
In addition, it is desired to provide a scrubber apparatus and process which advantageously removes phenolic containing dusts and mists with depositing characteristics from an inert gaseous process stream.